At present, it is necessary to prepare different substrates such as InGaN, GaN, GaAs and ZnO substrates to prepare blue, green and red light emitting diodes. Because different semiconductor film should be used for each light emitting diode, the current preparation process requires high cost facilities. Therefore, if blue, red and green light emitting diodes can be prepared from the same semiconductor film, manufacturing cost and investment cost can be reduced remarkably. At present, white light emitting diodes, which are gaining spotlight as backlight source for liquid crystal displays of lightings, notebooks, cell phones, etc., are prepared by adding a yellow light (560 nm) emitting YAG:Ce phosphor to a blue light emitting diode. Because white light emitting diodes prepared from blue light emitting diodes are excited by light having a wavelength ranging from 450 to 470 nm, only a limited number of phosphors can be used. That is, only YAG:Ce-based white light emitting diodes can be obtained using blue light emitting diodes having a wavelength range of from 450 to 470 nm. Therefore, there is an urgent need for the development of new phosphors other than YAG:Ce.
As UV light emitting diodes are developed as excitation light source, a new era has opened in making white light emitting diodes with single chips. That is, by using each of red, green and blue phosphors with a chip having light with a wavelength ranging from 380 to 410 nm as energy source, it has become possible to obtain a tri-color white light emitting diode with better luminescence strength and offering superior white color. Consequently, a phosphor that can be excited in the wavelength range of from 380 to 410 nm is required. Especially, a new phosphor emitting light in the range of from yellow to red is needed to obtain white light with good efficiency and high color rendering index (CRI).